Byron Irvine, Yantai Gan and Guy Lafond

AAFC- Brandon, Swift Current and Indian Head

email (204) 726-7650 birvine@em.agr.ca

Yields reductions resulting from delayed seeding, are associated with temperature stress, lodging, lack of timely weed control, and greater insect and disease pressure. Thus delayed seeding reduces yields even when crops are irrigated and do not lack moisture. Extreme drought or excess water may mask the effects of delayed seeding and in some years rainfall patterns will favour crops, which are seeded later. For Manitoba conditions "late seeding" will generally be after the third week of May. Flax, wheat, barley, pea and canola all show decreased yields from late seeding so the choice of which to seed first is a matter of which will cost the least. Barley seems to be less prone to yield reductions than other crops and there is evidence of variety differences in response to seeding date. Head to head comparisons of yield reductions for various crops are few but in one study at Swift Current delayed seeding reduced the yields of polish canola, lentil and mustards more than other crops. Under high moisture conditions delayed seeding will increase lodging and this will cause major reductions in yields. In many cases the total dry matter production will not decline significantly but grain yields will decline significantly indicating that photosynthesis is not limiting yields but rather the ability of the plant to move this material into seeds.

Early seeding can be accomplished by increasing the size of your equipment, increasing operating speed, use of fall or dormant crops and growing crops suited to later planting in your rotation. Higher operating speeds often result in uneven seeding and packing and is generally false economy. If labour is available longer hours of operation may be feasible. Zero tillage has a limited number of operations in the spring and thus aids in early seeding. However, since control of wild oats and volunteer cereals by preplant glyphosate application is greater after these plants have reached the second leaf stage this may delay seeding in a zero tillage system.

The chant "seed early, seed early, seed early" sounds like nails on chalkboard particularly after a spring like 1999. But it is exactly springs like 1999 that bring the need to rethink our cropping systems to allow early seeding of wheat, pea, flax and canola. Single pass low disturbance seeding systems go a long way towards this goal but are not the total answer.

Early seeding enhances yields in the following ways: avoidance of high temperature stress, fall frost, quality loss from poor drying late in the year, avoiding wheat midge damage and increasing the number of spraying days when the crop is in the optimum growth stage. In addition early seeding allows the crop canopy to be more fully developed in June when days are longest and the potential for photosynthesis is the greatest. The downside of early seeding is higher equipment or labour requirement and the potential for selection of weeds, which grow well at cooler temperatures, and the cost of controlling these weeds.

Over an 11 year period at Brandon wheat yields declined 11% when seeding was delayed from the first of May until the end of May and an additional 17% if planting was delayed into the second week of June (Table 1). Over the period of 1982-85 the yield of barley cultivars was reduced by an average of 31% when seeding was delay until the start of the second week of June but the range was from a 9% reduction to a 47% reduction for the highest yielding variety at the early seeding date. When seeded in early June Leduc barley produced 24% more grain than the average of the other cultivars even though its yields were 19% lower than at the early date. Under irrigated conditions in central Saskatchewan delaying seeding of wheat reduced seed yield by 13-25% depending on the variety. Biggar CPS wheat outyielded Roblin by 16% at the early seeding date but by only 9% at the later seeding date. While most of the wheat (except Roblin) lost about 20% of their yield from delayed seeding only Manley barley lost a similar amount of yield (Table 2). While it is clear that delayed seeding will reduce yields it should be possible to identify genotypes which limit this reduction will a reasonable testing effort. Since it is not possible to plant all crops early it would be an advantage for breeders to screen for types which have less reduction at later seeding dates. This would improve the potential for eliminating an in crop wild oat herbicide application without economic loss. Under irrigation the yield loss for Duke barley was 9 bu/ac or about $15/ac at current prices. If wild oat herbicides were removed the net cost would be equal. If seeding were delayed for weed control this would be economical marginal at low prices and result in significant losses at higher prices. There is sufficient genetic variation, even in currently available varieties, to suggest that significant progress could be made when more pressing issues like fusarium are under control. While delayed seeding will always result in a yield penalty and with crops such as wheat there may be a quality penalty due to frost and weathering protein levels may increase with delays in seeding which could offset yield concerns.

In a study conducted near Edmonton (Degenhart and Kondra 1981) found a 4% increase in the total dry matter produced from delayed seeding but a 20% decline in seed production(Table 4). This was not affected by variety or by altering seeding rate from 3 to 12 kg/ha. There was no impact of delayed seeding on seed size so the decline in yield was related to seeds per unit area. Similar yield reductions were found at Swift Current (Table 3). High temperatures, for even a short period near the start of flowering, can drastically reduce the number of seeds formed even when after the temperature stress is removed (Angadia et al 1999). Since temperature stress at a later growth stage is not as damaging to seed yields early planting increases the odds of temperature stress avoidance. In Swift Current Polish canola yields were reduced by 28% while Argentine canola had 16% lower yields at late rather than early seeding(Table 3). Lentil, polish canola and yellow mustard suffered 26-31% yield loss from delayed planting while hard red spring wheat yield were reduced less than 12%. Similar trials have not been conducted in Manitoba.

Delaying seeding from the first of May until the end of May reduced flax yields by 20% over a 9 year period in North Dakota (Table 6 ). Yields were reduced by 30% under irrigation in central Saskatchewan(Table 5). Delayed seeding resulted in taller plants and greater lodging under irrigated conditions. Norlin seems to have the same growing degree days to flower regardless of seeding date and yields reasonably well at even with a mid June planting. AC Linora and several new lines in testing appear to yield well when seeding is delayed.

High temperatures decrease the yields of cool season crops by shortening the growing period and by causing various physiological growth anomalies. The optimal temperature mean daily temperature for wheat ranges from 18-20 ^oC (64-68 ^oF). Each degree ^oC increase in the average daily temperature, above the optimum, decreased the length of the growing period for wheat by about 3 days and thus decreased grain size and yield. High temperatures during flowering may cause reductions in fertility. Pea and canola crops have been shown to be very sensitive to high temperatures during flowering and thus delayed seeding often causes serious yield losses due to the greater potential for high temperature stress resulting from delayed seeding.

There is overwhelming evidence that drought in the 3-4 week period prior to flowering reduces yields more than at any other part of the growing period. Drought is not just the amount of water available but also the potential rate at which water can be used. Even when the soil has adequate moisture to support growth the plant may be stressed due to water conducting tissues being unable to supply water at a high enough rate to meet the crops demand. High temperature and strong winds can cause induce visible wilting in crops such as fababean even though the soil is at field capacity. Under good moisture conditions delayed seeding reduces seed yields to a greater extent than dry matter production. This would indicate that in many cases there is sufficient energy to fill the seed but seed number or seed size limit the yield potential.

Vernalization and photoperiod affect the growth of cereal grain crops. Wheat varieties such as many of the Canadian CPS class have a vernalization requirement and thus have greatly delayed maturity and reduced yields when seeded late.

It is generally accepted that wild oats and volunteer cereals are poorly controlled if the Roundup burn off is applied prior to the second leaf stage. Delaying seeding until this time may result in reduced yields but not controlling them may be even worse. High temperatures increase the rate of crop and weed development. Thus delaying seeding decreases the number of spraying days when the weeds are small and actively growing. An additional factor is that the number of days with rainfall and the total amount of rainfall are greater in June than in May. At Brandon there are, on average, 2.5 days with rainfall of greater than 10 mm in the last 2 weeks of May while there are 4.0 days with this much rain in the first two weeks of June and 4.8 days in the last 2 weeks of June. Also weeds such as green foxtail and red root pigweed grow much more rapidly at high temperatures than at low temperatures and delayed seeding may increase their competitive effects.

The most expensive way of seeding early is to increase the size of your equipment. There are limits to the size of equipment and with zero tillage the ownership costs of a tractor are very large due to the low number of hours of use. A more cost effective system may be to seed as much of the crop in the fall as possible and spread out the workload. As you move farther north, seeding winter wheat is always a challenge since it conflicts with harvesting operations. It is my view that a dormant seeded oilseeds will allow these crops to be harvested in time to allow seeding of winter wheat. Since canola and wheat account for over 70% of most crop rotations in Manitoba, sowing a portion of these crops in the fall will free up considerably more time in the spring.

Dry bean acres could increase but market size and land suitability limit this expansion. In some areas of North Dakota soybeans are a viable crop and since they require a lot of heat and do not like spring frost they must be planted later.

Forage crops appear to have the greatest potential for limiting the amount of land that must be planted each year. They have the additional value in spreading out the harvest period or being harvested by animals which limits the overall costs. Crops such as alfalfa fix large amounts of nitrogen and if the marketing can be worked out there are major time savings in the spring. High transportation costs, relative to the value of the product, limit the export of hay to crops such as alfalfa cubes and compressed timothy hay. There are significant challenges to low cost beef production but with changes in freight rates and diseases in grain crops the value of season long pasture management may provide an economically attractive option, but it may or may not be attractive due to the change in lifestyle required.

Angadi, S.V., Cutforth, H.W, Miller, P.R. and McConkey, B. 1999. The effect of high temperature stress on Yield and yield components of three brassica species. Soils and Crops. p

Degenhardt, D.F. and Kondra, Z.P. 1981. The influence of seeding date and seeding rate on seed yield and yield components of five genotypes of Brassica napus. Can. J. Plant Sci. 61:175-183.

Thompson, C.R, Hoad, B.K. and Lukach, J.R. 1988 Flax variety response to planting date. North Dakota Farm Research 45: (5) 22-26.

Cereals program Johnston and Metcalfe

Irvine unpublished

Date 1: April 28 to May 5; Data 2: May 10 to 15; and Date 3: May 24 to 30, varying from year to year. Yanti Gan and Perry Miller